Atherosclerosis is a chronic inflammatory disease of the vessel wall. This proposal is directed towards understanding the contribution of extracellular nucleotide signaling through purinergic receptor to vascular inflammation and the development of atherosclerosis. Studies of a specific G protein-coupled nucleotide receptor (P2Y2R) have shown that when activated by adenosine 5'-triphosphate (ATP) in endothelial cells (EC), mediates monocyte recruitment through enhanced expression of vascular cell adhesion molecule-1 (VCAM-1). In addition, P2Y2R develop accelerated intimal lesions in response to vascular injury, whereas P2Y2R deficiency protects against intimal lesion growth. Furthermore, in absence of P2Y2R, apolipoprotein E (ApoE) deficient mice exhibit reduced atherosclerotic lesions and decreased inflammation reflected by lower macrophage content. Based upon these observations, we hypothesize the existence of differential P2Y2R-mediated effects on vascular and blood-derived cells that drive the progression of atherosclerosis. We have generated a genetically altered mouse with floxed P2Y2R alleles that allows for its targeted deletion in specific cells of interest. Using this novel reagent we propose first to evaluate the contribution f P2Y2R on blood-derived cells to atherosclerosis and identify the mechanisms by which P2Y2R regulates VCAM-1 shedding. We propose using bone marrow transplantation from ApoE-/- mice to P2Y2R-/-/ApoE-/- mice vice versa, to dissect the relative contribution of hematopoietic-derived cell P2Y2 R to atherosclerosis. Through use of in vitro cell-based systems in which we can examine the shedding of VCAM-1, we will be able to dissect how P2Y2R activation regulates the generation of soluble VCAM-1. We will determine whether endothelial cell-specific inactivation of P2Y2R prevents endothelial inflammatory phenotype and protects against atherosclerosis by assessing the inflammatory status of atherosclerotic lesions in mice with endothelial -/- cell-specific deletion of P2Y2R on ApoE background. We will also characterize the effects of smooth muscle cell- -/- specific deletion of P2Y2R on the development of atherosclerosis in ApoE mice by assessing collagen synthesis, cellular proliferation and determining plaque stability. Successful completion of the proposed studies will further our understanding of purinergic signaling in vascular inflammation, and could lead to new therapies for preventing and diagnosing atherosclerosis.